The present invention is in the field of waterwalls for twin tower gasification systems. More specifically, the invention is directed to a tubular waterwall, capable of carrying a coolant, for twin tower coal gasification systems.
Twin tower systems for coal gasification employ a radiant boiler tower and a convection boiler tower. These boilers are generally connected by a transfer duct. In the actual process of gasification, oxygen and a coal slurry are injected into a gasification zone above the radiant boiler tower wherein the coal slurry is ignited forming hot gas and molten slag. The hot gases flow downward and excess slag and soot fall to the bottom of the tower. The gas flows through the transfer or connecting duct to the convection boiler where the gas flows upward to the top of the convection boiler.
The temperature of the raw coal gas is sufficiently high to cause destructive thermal stresses on the internal surfaces of the towers and the connecting duct. Also the raw coal gas is corrosive. As such, tubular waterwalls carrying coolant are utilized to protect the walls of the boilers, to lower the temperature of the raw gas and to recover the transferred heat as saturated steam. Because of the harsh environment tubular waterwalls are subject to frequent failure. The failures generally occur at fittings and headers. Heretofore, an inordinate number of fittings and headers have been required in forming the liner. Thus, the number of points where failure is more likely is increased. When a fitting fails costly and time consuming replacement procedures are required. Also initial construction of these systems are complex resulting in high construction costs.